The main approaches to reduce the flammability of thermoplastic polyesters are melt additives, topical finish treatments, and copolymerization with flame resistant monomers. Melt additives generally include halogenated organic compounds with high levels of bromine or chlorine. A second component when halogenated compounds are employed is antimony trioxide (Sb.sub.2 O.sub.3). Other popular elements found in melt additives are phosphorus, molybdenum and nitrogen.
Phosphorus compounds are widely used to reduce the flammability of thermoplastic polymers. For example U.S. Pat. Nos. 3,987,008; 4,203,888; 4,517,355; and 4,940,772 disclose a broad variety of organic phosphor compounds in thermoplastic polyesters.
U.S. Pat. No. 3,987,008 discloses a polyphosphonate with arylene and haloarylene groups. U.S. Pat. No. 4,203,888 discloses an aryl diphosphate.
One disadvantage of these phosphorus compounds is that they are inert additives which build a separate phase in the thermoplastic polyesters with negative influence of their properties and a tendency to migrate to the surface.
U.S. Pat. No. 4,517,355 describes a linear polyester, which contains a phosphinic acid derivative bonded in the macromolecule.
U.S. Pat. No. 4,940,772 describes a process for producing a flame resistant polyester by copolymerizing a polyester with an unsaturated compound and reacting this copolyester with a specific phosphorus compound.
An object of the present invention was to provide a thermoplastic polyester with reduced flammability and simultaneous excellent physical properties.
Another object was to provide a process for the manufacture of a thermoplastic polyester with reduced flammability for the manufacture of molded articles by injection molding or extrusion.
Still another object was to provide a masterbatch of a thermoplastic polyester with reduced flammability.